In order to achieve power losses that are as small as possible integrated circuits (ICs) for controlling laser diodes are being developed for ever decreasing supply voltages. Breakdown criteria of many of the integrated components used constitute a further motivation for smaller supply voltages.
The operating point of the laser diode to be controlled is set by a threshold current and a modulation current, the modulation current representing the datastream. The currents generate a voltage drop across the laser diode. The voltage drop across the diode may be so large that the laser can no longer be driven directly by the laser driver IC on account of the limiting supply voltage.
If the voltage drop across the laser diode is so large that the laser can no longer be driven directly by the laser driver IC on account of the limited supply voltage or the necessary voltage drops across the driver transistors, then it is known to allow the modulation of the laser diode to be effected by means of a coupling capacitance. During the modulation and transmission of the data in the radio frequency range, however, losses and mismatches due to parasitic elements occur on the coupling paths both from the modulation output of the laser driver IC to the coupling capacitor and from the coupling capacitor to the laser diode coupling unit. These parasitic elements may be, inter alia, bonding wire inductances and pad capacitances.